Multi-wavelength Laser Inspection

ABSTRACT

An example system for inspecting a surface includes a laser, an optical system, a gated camera, and a control system. The laser is configured to emit pulses of light, with respective wavelengths of the pulses of light varying over time. The optical system includes at least one optical element, and is configured to direct light emitted by the laser to points along a scan line one point at a time. The gated camera is configured to record a fluorescent response of the surface from light having each wavelength of a plurality of wavelengths at each point along the scan line. The control system is configured to control the gated camera such that an aperture of the gated camera is open during fluorescence of the surface but closed during exposure of the surface to light emitted by the laser.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 16/890,950, filed Jun. 2, 2020 and issued as U.S. Pat. No.11,262,302, which is a divisional of U.S. patent application Ser. No.15/991,292, filed May 29, 2018 and issued as U.S. Pat. No. 10,705,019,the entire contents of each of which are hereby incorporated byreference.

FIELD

The present disclosure relates generally to fluorescent spectroscopy,and more particularly, to systems and methods for inspecting a surfaceusing fluorescent spectroscopy.

BACKGROUND

Molecules of some compounds can be excited from a ground state to anexcited state using a beam of light. During this excitation, individualmolecules absorb photons and shortly thereafter emit light having alonger wavelength than the beam of light. This emission of light afterabsorbing a photon is referred to as fluorescence.

Fluorescent spectroscopy is an inspection technique that involves theanalyzing the spectral distribution of light emitted by a sample due tofluorescence. In an example approach, a light source illuminates asample, causing some of the molecules within the sample to fluoresce. Adetector then measures characteristics of the fluorescence, such as theintensity and/or wavelength of the light emitted by the sample.

An emission spectrum of a sample can be generated by exciting a sampleat a particular wavelength and measuring the relative intensity offluorescence over a range of detection wavelengths. Additionally oralternatively, an excitation spectrum of a sample can be generated bymeasuring the relative intensity of fluorescence at a particularwavelength while the sample is excited over a range of excitationwavelengths.

SUMMARY

In one example, a system for inspecting a surface is described. Thesystem includes a laser, an optical system, a gated camera, and acontrol system. The laser is configured to emit light at a wavelengththat varies over time. The optical system includes at least one opticalelement, and is configured to direct light emitted by the laser topoints along a scan line during a plurality of time intervals such that:the wavelength of the light directed to each point along the scan linevaries from point to point within time intervals of the plurality oftime intervals, and over the plurality of time intervals, light havingeach wavelength of a plurality of wavelengths is directed to each pointalong the scan line. The gated camera is configured to record afluorescent response of the surface from the light having eachwavelength of the plurality of the plurality of wavelengths at eachpoint along the scan line. The control system is configured to controlthe wavelength of the light emitted by the laser and control gating ofthe gated camera.

In another example, a system for inspecting a surface is described. Thesystem includes a laser, an optical system, a gated camera, and acontrol system. The laser is configured to emit pulses of light, withrespective wavelengths of the pulses of light varying over time. Theoptical system includes at least one optical element, and is configuredto direct light emitted by the laser to points along a scan line onepoint at a time. The gated camera is configured to record a fluorescentresponse of the surface from light having each wavelength of a pluralityof wavelengths at each point along the scan line. The control system isconfigured to control the gated camera such that an aperture of thegated camera is open during fluorescence of the surface but closedduring exposure of the surface to light emitted by the laser.

In another example, a method for inspecting a surface is described. Themethod includes causing a laser to emit pulses of light havingrespective wavelengths that vary over time. The method also includesdirecting, using at least one optical element of an optical system, afirst pulse of light having a first wavelength to a first point along ascan line and a second pulse of light having a second wavelength to asecond point along the scan line. In addition, the method includesrecording, using a gated camera, a first fluorescent response of thesurface to the first pulse of light and a second fluorescent response ofthe surface to the second pulse of light. Further, the method includesdirecting, using the at least one optical element, a third pulse oflight having the first wavelength to the second point and a fourth pulseof light having the second wavelength to the first point. Still further,the method includes recording, using the gated camera, a thirdfluorescent response of the surface to the third pulse of light and afourth fluorescent response of the surface to the fourth pulse of light.

The features, functions, and advantages that have been discussed can beachieved independently in various examples or may be combined in yetother examples further details of which can be seen with reference tothe following description and figures.

BRIEF DESCRIPTION OF THE FIGURES

The novel features believed characteristic of the illustrative examplesare set forth in the appended claims. The illustrative examples,however, as well as a preferred mode of use, further objectives anddescriptions thereof, will best be understood by reference to thefollowing detailed description of an illustrative example of the presentdisclosure when read in conjunction with the accompanying figures,wherein:

FIG. 1 illustrates an example system, according to an example.

FIG. 2 illustrates another example system, according to an example.

FIG. 3 is an example synchronization diagram, according to an example.

FIG. 4 is an example energy level diagram, according to an example.

FIG. 5 shows a flowchart of an example method, according to an example.

FIG. 6 shows an additional operation for use with the method shown inFIG. 6, according to an example.

FIG. 7 shows a flowchart of another example method, according to anexample.

DETAILED DESCRIPTION

Disclosed examples will now be described more fully hereinafter withreference to the accompanying figures, in which some, but not all of thedisclosed examples are shown. Indeed, several different examples may beprovided and should not be construed as limited to the examples setforth herein. Rather, these examples are provided so that thisdisclosure will be thorough and complete and will fully convey the scopeof the disclosure to those skilled in the art.

Described herein are systems and methods for inspecting a surface. Thesystems and methods can be used to rapidly scan a surface, such as thesurface of a composite part, to identify any materials on its surfacevia fluorescent spectroscopy. For instance, the systems and methods canbe used to determine the cleanliness of a surface, which may bebeneficial during preparation of a surface for sealing, painting,priming, and bonding operations.

An example system may include a laser configured to emit light at awavelength that varies over time, an optical system, a gated camera, anda control system. The laser can include a transducer configured toexcite a pressure wave down a length of a lasing medium of the lasersuch that the pressure wave modifies energy levels of the lasing mediumover time, thereby altering the wavelength of the light emitted by thelaser. The optical system can include at least one optical element thatguides light emitted by the laser towards a surface of a part. Forinstance, the optical system can be configured to direct light emittedby the laser to points along a scan line during a plurality of timeintervals such that: (i) the wavelength of the light directed to eachpoint along the scan line varies from point to point within timeintervals of the plurality of time intervals, and (ii) over theplurality of time intervals, light having each wavelength of a pluralityof wavelengths is directed to each point along the scan line.

The gated camera can be configured to record a fluorescent response ofthe surface from the light emitted by the laser. For instance, the gatedcamera can be configured to record a fluorescent response of the surfacefrom light having each wavelength of the plurality of wavelengths ateach point along the scan line. To accomplish this, the control systemcan be configured to synchronize operation of the laser with operationof the gated camera. For instance, the control system can be configuredto control a shutter of the laser and an electronic gating system of thegated camera such that an aperture of the gated camera is open to lightduring fluorescence of the surface but closed during exposure of thesurface to light emitted by the laser.

Advantageously, fluorescent responses obtained using the systems andmethods disclosed herein can yield a higher signal-to-noise ratio (SNR)than fluorescent responses that can be obtained using ordinaryfluorescent spectroscopy. With ordinary fluorescent spectroscopy, anentire surface is illuminated at once. On the other hand, the describedsystems and methods can operate by shining a pulse of light having arelatively small spot size at points along a scan line one point at atime. With the described systems and methods, the intensity of theapplied light, and therefore the intensity of the fluoresced light, canbe much higher than intensity that can be obtained when illuminating theentire surface at once.

Further, the level of noise in the fluorescent response can be less thanthe level of noise in fluorescent responses obtained using ordinaryfluorescent spectroscopy. By shining light having individual wavelengthsof a range of wavelengths one at a time rather than shining light havinga broad spectrum, the described systems and methods can avoid shiningany light at the fluorescent wavelengths when the surface material isfluorescing. In addition, the synchronization of the laser with thegated camera can also decrease the level of noise. While the gatedcamera's aperture is open to light, the laser light can be blocked by ashutter of the laser.

The described systems and methods can also apply a high power beam oflight to a spot on a surface without damaging the surface. If light iscontinuously applied to a small spot on a surface, the surface canbecome overheated, and potentially be damaged. The described systems andmethods can help to avoid this problem in various ways. For example, thelaser can be shuttered so that the laser emits pulses of light and thelong term time-averaged intensity on the surface is moderate even whilethe instantaneous intensity of each pulse is high. Additionally oralternatively, the light emitted by the laser can pass through a prismwhich changes the point that the laser light strikes the surface of apart as the wavelength of the light emitted by the laser changes.

The described systems and methods can also yield more chemicalinformation about materials on a surface than ordinary fluorescentspectroscopy. Ordinarily, white (i.e., broad spectrum) light is shown ona surface. The fluorescent response to the light therefore providesinformation about the surface's response to a broad spectrum ofwavelengths. Whereas, with the described systems and methods, lighthaving a particular wavelength of a range of wavelengths can be shown ona surface, with that wavelength changing over time. The resultingfluorescent response therefore provides information about how thesurface, including any materials on the surface, responds to eachwavelength individually. As a result, the described systems and methodscan be used to build a superior chemical signature, as compared totraditional fluorescent spectroscopy.

Various other features of these systems and methods are describedhereinafter with reference to the accompanying figures.

Referring now to FIG. 1, FIG. 1 illustrates an example system 100,according to an example embodiment. In line with the discussion above,system 100 can be used to inspect a part 102. For example, system 100can be used to inspect part 102 to identify any materials on a surface104 of part 102. As shown in FIG. 1, system 100 includes a laser 106, anoptical system 108, a gated camera 110, and a control system 112.

Laser 106 can be configured to emit light at a wavelength that variesover time. Laser 106 can include an excitation source, or pump,configured to beam energy into a lasing medium. In one example, thelasing medium can absorb the energy, exciting electrons in the lasingmedium from a first energy state (ground state) to a third energy state(pump level). The electrons can then relax to a second energy state,undergoing what is sometimes referred to as a radiation-less transition.In addition, an electron in the second energy state may decay byspontaneous emission to the first energy state, releasing a photon. Theenergy of the photon, and therefore the wavelength of the photon,corresponds to a difference between the second energy state and thefirst energy state. Laser 106 can also include a dielectric mirror 107that reflects light back into the lasing medium in order to stimulatemore emission of photons and increase an intensity of the light emittedby laser 106.

Laser 106 can also include a transducer 109 configured to excite apressure wave down a length of the lasing medium, parallel to thedirection of stimulated emission of light. A pressure wave in a solidmedium pushes atoms within that medium together, shortening theirseparation. The pressure wave within the lasing medium can thereforepush atoms together within the lasing medium, shortening theirseparation. The change in separation can alter the energy levels of thefirst, second, and third energy states. The change in separation occurson a time scale that is slower with respect to the absorption andemission of light. Therefore, as the pressure wave alters the energylevels of the first, second, and third energy states, the pressure wavealters the difference between the first and second energy states, andalters the wavelength of light emitted by laser 106. As the pressurewave continues to move across the lasing medium, the pressure wave cancontinue to alter the energy levels of the first and second energystates, and alter the wavelength of light emitted by laser 106. Thus,transducer 109 operating on the lasing medium can enable laser 106 toemit a continuously varying, controlled, predictable range ofwavelengths of light.

Likewise, dielectric mirror 107 can experience the same pressure waveand be compressed and stretched with the lasing medium. Expanding thedielectric mirror's physical dimension can change an index of refractionand depth of the dielectric mirror, thereby changing the frequency oflight that gets primarily reflected in order to increase an intensity oflaser 106. The material of the dielectric mirror can be chosen such thatthe response of the dielectric mirror to the pressure wave approximatelymatches the response of the lasing medium to the pressure wave.

As a particular example, laser 106 can be a ruby laser configured toemit a 694.3 nanometer laser beam. The lasing medium of the ruby laser(a ruby crystal) can have a 345 gigapascals (GPa) Young's modulus, a 2.1GPa tensile strength, a 4.75 angstrom lattice constant in a firstdirection, and a 12.98 angstrom lattice constant in a second direction.With this configuration, the lasing medium of the ruby laser can bestretched by 2.1/345 (approximately 0.6%) before it may “break”.Breaking refers to a point where the interaction between neighboringatoms becomes so weak that relative motion of the atoms is no longerconstrained. And, in any material, the strength of the interactionbetween atoms is defined by the energy levels of the shared electrons.

The ruby crystal may have a second energy state and a first energy stateseparated by 1.79 electron volts (eV) corresponding to a wavelength of694.3 nanometers in an unstretched state. As the ruby crystal stretchesand the interatomic separation increases, the energy gap between thesecond energy state and the first energy state can decrease with theincreased separation, such that the wavelength increases. Hence, apressure wave could cause the ruby crystal to stretch, and produce lighthaving a wavelength greater than 694.3 nm. Similarly, the ruby crystalcould be compressed by the pressure wave, causing the wavelength oflight emitted by the laser to decrease below 694.3 nm.

In other examples, laser 106 could be a semiconductor laser. Forexample, laser 106 could be an indium gallium nitride (InGaN) laser thatlases at around 405 nm, a gallium indium phosphide (GaInP) or aluminumgallium indium phosphide (AlGaInP) laser that lases at around 650 nm, ora gallium aluminum arsenide (GaAlAs) laser that lases at around 785 nm.Hence, the example of the ruby laser is not meant to be limiting.

In some examples, laser 106 can include a shutter 114. Shutter 114 canbe controlled electronically by control system 112 and synchronized withthe transducer, so that the shutter intermittingly blocks light emittedby the laser. In other words, shutter 114 can be controlled so thatlaser 106 emits time-separated pulses of light, with the wavelengths ofthe pulses of light varying over time. By way of example, FIG. 1 depictsa first pulse 116 a having a first wavelength, a second pulse 116 bhaving a second wavelength, and a third pulse 116 c having a thirdwavelength.

Laser 106 can also include a filter 116. Filter 116 can be configured tofilter the wavelength of light that passes through to optical system108. For instance, filter 116 can filter out light having wavelengthabove an upper frequency and/or cut off light having a wavelength belowa lower frequency. In one example, filter could be a wedge-taperedmulti-layer interference filter.

Optical system 108 can be configured to spread out in space differentwavelengths of light emitted by laser 106. For instance, optical systemcan be configured to direct light emitted by laser 106 to points along ascan line 117. In one example, optical system 108 can be configured todirect light emitted by laser 106 to points along scan line 117 during aplurality of time intervals such that: (i) the wavelength of the lightdirected to each point along scan line 117 varies from point to pointwithin time intervals of the plurality of time intervals, and (ii) overthe plurality of time intervals, light having each wavelength of aplurality of wavelengths is directed to each point along scan line 117.

Optical system 108 could cause points along scan line 117 to beilluminated one point at a time with light having a single wavelength ofthe plurality of wavelengths. For instance, optical system 108 caninclude a first scanning mirror 120 and a second scanning mirror 122that are controllable by control system 112. During a first timeinterval, first scanning mirror 120 can spread out first, second, andthird pulses 116 a-c to respective points along scan line 117. In orderto achieve this, first scanning mirror 120 can be at a first positionwhen first pulse 116 a contacts first scanning mirror 120, such thatfirst pulse 116 a reflects off of second scanning mirror 122 andcontacts a first point along scan line 117. First scanning mirror 120can then rotate to a second position when second pulse 116 b contactsfirst scanning mirror 120, so that second pulse 116 b reflects off ofsecond scanning mirror 122 and contacts a second point along scan line117. Further, first scanning mirror 120 can then rotate to a thirdposition when third pulse 116 c contacts first scanning mirror 120, sothat third pulse 116 c reflects off of second scanning mirror 122 andcontacts a third point along scan line 117.

During a second time interval, first scanning mirror 120 can becontrolled to translate the illumination points for the first, second,and third pulses 116 a-c along scan line 117. For instance, firstscanning mirror 120 can be controlled so that first pulse 116 a contactsthe second point, second pulse 116 b contacts the third point, and thirdpulse 116 c contacts the first point. Similarly, during a third timeinterval, first scanning mirror 120 can be controlled to translate theillumination points again. In other words, first scanning mirror 120 canbe controlled so that each of three points along scan line 117 isindividually illuminated by each of the first, second, and third pulses116 a-c. In practice, the number of points along a scan line could begreater than three. For instance, the number of points could be 10, 50,100, or more.

Second scanning mirror 122 can be configured to translate the scan line.For instance, after each of three points along the scan line isindividually illuminated by each of the first, second, and third pulses116 a-c, second scanning mirror 122 can rotate to a different positionso that the scan line advances along surface 104. In this manner, secondscanning mirror 122 can translate the scan line from a first segment onsurface 104 to a second segment on surface 104.

Gated camera 110 can be configured to record a fluorescent response ofsurface 104 from light emitted by laser 106. For instance, gated camera110 can be configured to record a fluorescent response of surface 104from light having each wavelength of the plurality of wavelengths ateach point along the scan line. As used herein, the fluorescent responseof surface 104 may refer to a fluorescent response of surface 104 itselfor a fluorescent response of a material, such as a surface contaminant,that is present on surface 104.

In one example, gated camera 110 can include an image intensifier 111configured to increase an intensity of available light that is receivedat gated camera 110. For instance, image intensifier 111 can be anoptoelectronic device that converts photons emitted by materials onsurface 104 into electrons, amplifies those electrons, and then convertsthe electrons back into photons of light.

Gated camera 110 can be electronically-gated. For instance, gated camera110 can include an electronic gating system that functions like a camerashutter, allowing light to be received through an aperture of gatedcamera 110 when the electronic gate is enabled but preventing light frompassing through the aperture of gated camera 110 when the electronicgate is disabled. The gating duration could be very short, such as a fewnanoseconds or even a few picoseconds. The electronic gating system caninclude high-speed digital delay generators, which allow a controlsystem to specify when the electronic gate is enabled and/or disabledrelative to the start of an event. The gating of the electronic gatingsystem could be controlled by control system 112. In one example, theelectronic gating system could be part of image intensifier 111. Forinstance, image intensifier 111 could be an electronically-gated imageintensifier. The electronically-gated image intensifier can include oneor more lenses, a photocathode, a microchannel plate, a phosphor screen,and electronics for providing different voltage biases to thephotocathode, microchannel plate, and phospher screen.

In an example configuration, laser 106, optical system 108, and gatedcamera 110 can be mounted to an apparatus, such as a housing, frame, orother support structure. Part 102 could then be brought near (e.g.,under) the apparatus for inspection. Additionally or alternatively, theapparatus can be portable, and can be moved to a location of part 102for in order to inspect part 102.

Control system 112 can include a processor 113 and a non-transitorycomputer-readable medium storing program instructions that areexecutable by processor 113 to carry out any of the control systemfunctions described herein. Processor 113 could be any type ofprocessor, such as a microprocessor, digital signal processor, multicoreprocessor, etc. Alternatively, the control system 112 could include agroup of processors that are configured to execute the programinstructions, or multiple groups of processors that are configured toexecute respective program instructions.

Control system 112 can include a computing device such as a laptopcomputer, mobile computer, wearable computer, tablet computer, desktopcomputer, or other type of computing device. As such, control system 112can include a display, an input device, and one or more communicationports through which the control system is configured to communicate withother devices of system 100 as well as devices that are not part ofsystem 100.

Control system 112 can be connected to laser 106, optical system 108,and gated camera 110 by way of one or more wired or wirelesscommunication links. In this manner, control system 112 can send data toand/or receive data from laser 106, optical system 108, and gated camera110.

In line with the discussion above, control system 112 can be configuredto control the wavelength of light emitted by laser 106 and controlgating of gated camera 110. In this regard, control system 112 can beconfigured to control a transducer that provides a pressure wave withina lasing medium of laser 106. Control system 112 can also be configuredto control shutter 114 of laser 106 such that shutter 114 intermittinglyblocks light emitted by the laser, yielding pulses of light. Inaddition, control system 112 can be configured to control shutter 114such that shutter 114 blocks light emitted by laser 106 when an apertureof gated camera 110 is open to light.

Further, control system 112 can be configured to control an electronicgating system of gated camera 110. When light impinges on surface 104,light is absorbed by surface 104. A predictable time after the arrivalof that light, the surface 104 may fluoresce, releasing light at avariety of frequencies. Control system 112 can control the electronicgating system of gated camera 110 such that the aperture of gated camera110 is open during fluorescence but closed during exposure of surface104 to the light from laser 106. This synchronization can allow gatedcamera 110 to detect only fluorescing light and not reflected light fromlaser 106.

In addition, a processor of control system 112, or a processor ofanother computing device, can be configured to identify a material onsurface 104 by analyzing fluorescent responses of surface 104 recordedby gated camera 110. For example, the fluorescent responses collected ata given point on surface 104, across a variety of excitationwavelengths, can be used to determine the chemical composition ofsurface 104. The chemical composition of surface 104 may be indicativeof whether a material, such as a cutting liquid, water, plastic, orother agent is present on surface 104 at the given point.

FIG. 2 illustrates another example system 200, according to an exampleembodiment. Like system 100 of FIG. 1, system 200 can be used to inspecta part 202. For example, system 200 can be used to inspect part 202 toidentify any materials on a surface 204 of part 202. Like system 100 ofFIG. 1, system 200 includes a laser 206, an optical system 208, a gatedcamera 210, and a control system 212. However, unlike optical system 108of FIG. 1, which includes first scanning mirror 120 and second scanningmirror 122, optical system 208 instead includes a prism 224 and ascanning mirror 222.

Prism 224 can be configured to cause the wavelength of the lightdirected to each point along scan line 217 to vary from point to pointwithin time intervals of a plurality of time intervals. For instance,prism 224 can be configured to cause first, second, and third pulses 216a-c to illuminate first, second, and third illumination points,respectively, along scan line 217 during a first time interval. Scanningmirror 222 can then be configured to translate the illumination pointsfor the first, second, and third pulses 216 a-c along scan line 217 fora subsequent time interval. Like second scanning mirror 122 of FIG. 1,scanning mirror 222 can also be configured to translate scan line 217from a first segment on surface 204 to a second segment on surface 204.For instance, scanning mirror 222 can be configured to translate scanline 217 after light having each wavelength of a plurality ofwavelengths is directed to each point along scan line 217.

FIG. 3 is an example synchronization diagram 300, according to anexample embodiment. Synchronization diagram 300 shows one possiblemanner of synchronizing operation of a laser, such as laser 106 of FIG.1 or laser 206 of FIG. 2, with a gated camera, such as gated camera 110of FIG. 1 or gated camera 210 of FIG. 2. In line with the discussionabove, a transducer 302 could excite a pressure wave within a lasingmedium 304 of a laser, and the laser could be shuttered, so that thelaser provides four pulses of light having four different wavelengths.Shortly after each pulse impinges on a surface of a part, the surfacecould provide a fluorescent response. In order to capture thefluorescent responses, but ignore reflections from the laser pulses, anelectronic gating system of the gated camera could be enabled (oropened) at a time that corresponds to when the fluorescent responsesoccur, but disabled (or closed) at other times when laser pulses areemitted. Further, the gated camera could capture frames of image data ata fixed rate.

As shown in FIG. 3, due to the operation of the electronic gatingsystem, “camera frame 1” might not include any fluorescent response datasince the camera gate is disabled. Other camera frames, however, couldinclude fluorescent response data. In particular, “camera frame 2” couldinclude a fluorescent response to a first pulse, “camera frame 3” couldinclude a fluorescent response to a second pulse, “camera frame 4” couldinclude a fluorescent response to a third pulse, and “camera frame 5”could include a fluorescent response to a fourth pulse.

In another example, a shutter of the laser could be controlled such thatmultiple pulses having the same wavelength of light are emitted insequence. For instance, the shutter of the laser could be controlled soas to be open whenever light emitted by the laser has a particularwavelength, but closed when light emitted by the laser has a wavelengthother than the particular wavelength. After capturing fluorescentresponse data for the multiple pulses, a processor can then performtime-averaging on the captured data, consistent with the number of laserpulses. For instance, if there were four pulses, the processor couldcombine the fluorescent response data from each of the four pulses, anddivide the fluorescent response data by four. This time-averaging canhelp to increase the SNR of the fluorescent response data.

FIG. 4 is an example energy level diagram 400. Energy level diagram 400shows how the energy levels of a semiconductor, referred to as theconduction band and valence band, can change as a function ofinteratomic distance. The semiconductor may be a lasing medium of alaser, for example.

Semiconductors include energy levels referred to as a conduction bandand a valence band. And, in a semiconductor laser, a photon is emittedwhen an electron drops from the conduction band to the valence band. Asinteratomic separation between atoms increases, the gap between theconduction band and the valence band decreases. Further, when the atomsare sufficiently separated such that the valence band is lower than theconduction band, the electrons can be localized to a single atom that isno longer part of the material.

As shown in FIG. 4, for an example semiconductor, at an interatomicdistance a, there is a band gap between the conduction band and thevalence band. When the semiconductor is stretched such that theinteratomic distance increases to a distance that is greater than a, theband gap decreases. In other words, stretching a semiconductor lasingmedium of a laser can cause the wavelength of light emitted by asemiconductor laser to increase. Conversely, when the semiconductor iscompressed such that the interatomic distance decreases to a distancethat is less than a, the band gap increases. Hence, compressing asemiconductor lasing medium of a laser can cause the wavelength of lightemitted by a semiconductor laser to decrease.

FIG. 5 shows a flowchart of an example method. Method 500 shown in FIG.5 presents an embodiment of a method that, for example, could be usedwith one of the systems shown in FIGS. 1 and 2, for example, or any ofthe systems disclosed herein. Any of the example devices or systemsdescribed herein, such as control system 112 of FIG. 1 or control system112 of FIG. 2, may be used or configured to perform logical functionspresented in FIG. 5.

Method 500 can include one or more operations, functions, or actions asillustrated by one or more of blocks 502-510. Although these blocks areillustrated in a sequential order, these blocks may also be performed inparallel, and/or in a different order than those described herein. Also,the various blocks may be combined into fewer blocks, divided intoadditional blocks, and/or removed based upon the desired implementation.

It should be understood that for this and other processes and methodsdisclosed herein, flowcharts show functionality and operation of onepossible implementation of present embodiments. In this regard, eachblock may represent a module, a segment, or a portion of program code,which includes one or more instructions executable by a processor forimplementing specific logical functions or steps in the process. Theprogram code may be stored on any type of computer readable medium ordata storage, for example, such as a storage device including a disk orhard drive. The computer readable medium may include non-transitorycomputer readable medium or memory, for example, such as computerreadable media that stores data for short periods of time like registermemory, processor cache, and RAM. The computer readable media may alsobe any other volatile or non-volatile storage systems. The computerreadable medium may be considered a tangible computer readable storagemedium, for example.

Initially, at block 502, the method 500 includes causing a laser to emitpulses of light having respective wavelengths that vary over time. Acontrol system could cause a transducer to excite a pressure wave down alength of a lasing medium of the laser, such that the pressure wavemodifies energy levels of the lasing medium over time and alters thewavelength of the light emitted by the laser. In addition, the controlsystem could control a shutter of the laser such that the shutterintermittingly blocks light emitted by the laser, yielding pulses oflight.

At block 504, the method 500 includes directing, using at least oneoptical element of an optical system, a first pulse of light having afirst wavelength to a first point along a scan line and a second pulseof light having a second wavelength to a second point along the scanline. The first pulse of light and the second pulse of light could passthrough a prism of the optical system so that the first pulse of lightand the second pulse of light are spread out in space. Alternatively, ascanning mirror of the optical system could separate the first pulse oflight and the second pulse of light in space. For instance, a controlsystem could control the scanning mirror so that the scanning mirror isin a first position when the first pulse of light impinges on thescanning mirror, and the scanning mirror is in a second position whenthe second pulse of light impinges on the scanning mirror.

At block 506, the method 500 includes recording, using a gated camera, afirst fluorescent response of the surface to the first pulse of lightand a second fluorescent response of the surface to the second pulse oflight.

At block 508, the method 500 includes directing, using the at least oneoptical element, a third pulse of light having the first wavelength tothe second point and a fourth pulse of light having the secondwavelength to the first point. In line with the discussion above, acontrol system could control a scanning mirror so that the scanningmirror is in the second position when the third pulse impinges on thescanning mirror and the scanning mirror is in the first position whenthe fourth pulse impinges on the scanning mirror.

And at block 510, the method 500 includes recording, using the gatedcamera, a third fluorescent response of the surface to the third pulseof light and a fourth fluorescent response of the surface to the fourthpulse of light.

FIG. 6 shows an additional operation for use with the method shown inFIG. 6. Block 602 of FIG. 6 could be performed as part of block 506 ofFIG. 5 and/or as part of block 510 of FIG. 5.

At block 602, FIG. 6 includes controlling an image intensifier of thegated camera such that an aperture of the gated camera is closed duringexposure of the surface to the pulses of light emitted by the laser. Byway of example, a control system could provide a command signal to anelectronic gating system of the image intensifier that causes anelectronic gate of the image intensifier to be disabled. The disablingof the electronic gate could coincide with times when a shutter of thelaser is opened. On the other hand, the control system could provide adifferent command signal to the electronic gating system of the imageintensifier that causes the electronic gate to be enabled at a shorttime (e.g., less than a nanosecond, one nanosecond, a few nanoseconds)after the shutter of the laser transitions from open to closed or at ashort time after the shutter of the laser transitions from closed toopen.

FIG. 7 shows a flowchart of another example method. Method 700 shown inFIG. 7 presents an example of a method that, for example, could be usedwith one of the systems shown in FIGS. 1 and 2, for example, or any ofthe systems disclosed herein. Any of the example devices or systemsdescribed herein, such as control system 112 of FIG. 1 or control system212 of FIG. 2, may be used or configured to perform logical functionspresented in FIG. 7. Method 700 may include one or more operations,functions, or actions as illustrated by one or more of blocks 702-710.Although these blocks are illustrated in a sequential order, theseblocks may also be performed in parallel, and/or in a different orderthan those described herein. Also, the various blocks may be combinedinto fewer blocks, divided into additional blocks, and/or removed basedupon the desired implementation. Each block may represent a module,segment, or a portion of program code, which includes one or moreinstructions executable by a processor for implementing specific logicalfunctions or steps in the process.

Method 700 could be combined with one or more blocks of method 500 ofFIG. 5.

Initially, at block 702, the method 700 involves receiving fluorescentresponse data for a surface of a part. For instance, the fluorescentresponse data could be fluorescent responses of the surface at a pointalong a scan line, fluorescent responses of the surface at multiplepoints along a scan line, or fluorescent responses of the surface atpoints along multiple scan lines.

At block 704, the method 700 involves identifying material(s) on thesurface of the part using the fluorescent response data. Identifyingmaterial(s) on the surface of the part may involve comparing thefluorescent response data to chemical signatures stored in a database ofknown chemical signatures.

At block 706, the method 700 involves determining whether or not theidentified material(s) on the surface are acceptable. Determiningwhether or not the identified material(s) on the surface are acceptablemay involve comparing the identified materials to a list of acceptablematerials, or comparing the identified materials to a list ofnon-acceptable materials.

If the identified material(s) are acceptable, then, at block 708, anacceptance indication may be provided. For instance, a control systemmay cause an audio element (e.g., a speaker or a buzzer) to provide anaudible acceptance indication and/or cause a lighting element (e.g., alight-emitting diode or a display) to provide a visual acceptanceindication. Whereas, if the identified material(s) are not acceptable,then, at block 710, a rejection indication may be provided. Like theacceptance indication, the rejection indication may be an audibleindication or a visual indication.

The providing of the acceptance indication may be optional. Forinstance, a control system may be configured to not provide anyindication if the identified material(s) acceptable, but to provide arejection indication if one or more of the identified materials arenot-acceptable.

The description of the different advantageous arrangements has beenpresented for purposes of illustration and description, and is notintended to be exhaustive or limited to the examples in the formdisclosed. After reviewing and understanding the foregoing disclosure,many modifications and variations will be apparent to those of ordinaryskill in the art. Further, different examples may provide differentadvantages as compared to other examples. The example or examplesselected are chosen and described in order to best explain theprinciples, the practical application, and to enable others of ordinaryskill in the art to understand the disclosure for various examples withvarious modifications as are suited to the particular use contemplated.

1-20. (canceled)
 21. A system for inspecting a surface, comprising: an optical system including at least one optical element, the optical system configured to: direct a first pulse of light having a first wavelength to a first point along a scan line and a second pulse of light having a second wavelength to a second point along the scan line during a first time period, and direct a third pulse of light having the first wavelength to the second point and a fourth pulse of light having the second wavelength to the first point during a second time period; and a gated camera configured to: record a first fluorescent response of the surface to the first pulse of light and a second fluorescent response of the surface to the second pulse of light, and record a third fluorescent response of the surface to the third pulse of light and a fourth fluorescent response of the surface to the fourth pulse of light.
 22. The system of claim 21, wherein: the gated camera comprises an image intensifier, and the system further comprises a control system configured to control the image intensifier such that an aperture of the gated camera is closed during exposure of the surface to the pulses of light.
 23. The system of claim 21, further comprising a laser configured to emit the first pulse of light and the third pulse of light.
 24. The system of claim 23, wherein: the laser comprises a shutter, and the system further comprises a control system configured to control the shutter such that the shutter intermittingly blocks light emitted by the laser, yielding pulses of light.
 25. The system of claim 24, wherein the control system is configured to control the shutter such that the shutter blocks light emitted by the laser when an aperture of the gated camera is open.
 26. The system of claim 21, wherein directing the first pulse of light to the first point along the scan line and the second pulse of light to the second point along the scan line comprises passing the first pulse of light and the second pulse of light through a prism.
 27. The system of claim 21, wherein directing the first pulse of light to the first point along the scan line and the second pulse of light to the second point along the scan line comprises controlling a scanning mirror such that the scanning mirror is in a first position when the first pulse of light impinges on the scanning mirror and the scanning mirror is in a second position when the second pulse of light impinges on the scanning mirror.
 28. The system of claim 27, wherein directing the third pulse of light to the second point along the scan line and the fourth pulse of light to the first point along the scan line comprises controlling the scanning mirror such that the scanning mirror is in the second position when the third pulse of light impinges on the scanning mirror and the scanning mirror is in the first position when the second pulse of light impinges on the scanning mirror.
 29. The system of claim 21, further comprising a control system configured to identify a material on the surface by analyzing the first fluorescent response and the fourth fluorescent response.
 30. The system of claim 29, wherein identifying the material on the surface comprises comparing the first fluorescent response and the fourth fluorescent response to chemical signatures stored in a database of known chemical signatures.
 31. The system of claim 29, wherein the control system is further configured to: determine that the identified material is an acceptable material; and based on the determining, provide an acceptance indication.
 32. The system of claim 29, wherein the control system is further configured to: determine that the identified material is not an acceptable material; and based on the determining, provide a rejection indication.
 33. A system for inspecting a surface, comprising: an optical system including at least one optical element, the optical system configured to direct light pulses to points along a scan line during a plurality of time intervals such that: the wavelength of the light directed to each point along the scan line varies from point to point within time intervals of the plurality of time intervals, and over the plurality of time intervals, light having each wavelength of a plurality of wavelengths is directed to each point along the scan line; and a gated camera configured to record a fluorescent response of the surface from the light having each wavelength of the plurality of wavelengths at each point along the scan line.
 34. The system of claim 33, configured such that the points along the scan line are illuminated one point at a time with light having a single wavelength of the plurality of wavelengths during the plurality of time intervals.
 35. The system of claim 33, wherein the at least one optical element comprises a prism configured to cause the wavelength of the light directed to each point along the scan line to vary from point to point within the time intervals of the plurality of time intervals.
 36. The system of claim 33, wherein the at least one optical element comprises a scanning mirror configured to cause the wavelength of the light directed to each point along the scan line to vary from point to point within the time intervals of the plurality of time intervals.
 37. The system of claim 33, wherein the at least one optical element comprises a scanning mirror configured to translate the scan line from a first segment on the surface to a second segment on the surface after light having each wavelength of the plurality of wavelengths is directed to each point along the scan line.
 38. The system of claim 33, further comprising at least one processor configured to identify a material on the surface by analyzing fluorescent responses recorded by the gated camera.
 39. A system for inspecting a surface, comprising: an optical system including at least one optical element; a gated camera; and a control system configured to perform a set of acts comprising: an optical system including at least one optical element, the optical system configured to: causing the at least one optical element to direct a first pulse of light having a first wavelength to a first point along a scan line and a second pulse of light having a second wavelength to a second point along the scan line, causing the gated camera to record a first fluorescent response of the surface to the first pulse of light and a second fluorescent response of the surface to the second pulse of light, causing the at least one optical element to direct a third pulse of light having the first wavelength to the second point and a fourth pulse of light having the second wavelength to the first point, and causing the gated camera to record a third fluorescent response of the surface to the third pulse of light and a fourth fluorescent response of the surface to the fourth pulse of light.
 40. The system of claim 39, wherein the set of acts further comprise controlling an aperture of the gated camera such that the aperture is closed during exposure of the surface to the first pulse of light and the second pulse of light. 